1. Field of the Invention
The present invention relates a light emitting element having a layer containing a light emitting substance formed between a pair of electrodes, a light emitting device including the light emitting element, and an electronic appliance.
2. Description of the Related Art
A light emitting element, which has recently been attracting attention as a pixel of a display device or a light source of a lighting device, has a light emitting layer between a pair of electrodes. When current flows between the pair of electrodes, a light emitting substance contained in the light emitting layer emits light.
In development of such a light emitting element, one of important problems is to prevent short-circuiting caused between a pair of electrodes of the light emitting element. One reason of shirt-circuiting caused between a pair of electrodes is a projection generated on each surface of the electrodes. Such a projection is generated when ITO and the like are crystallized, for example. The short-circuiting between the pair of electrodes can be suppressed by reducing roughness of each surface of the electrodes by covering the projection with a thick layer. However, by providing the thick layer, driving voltage of the light emitting element is sometimes increased. Therefore, a technique by which a thick layer is provided without increasing driving voltage has been developed. For example, patent document 1 discloses a technique by which a mixed film in which divanadium pentoxide and α-NPD (note that, α-NPD is also referred to as NPB) are mixed is provided. It is suggested that the short-circuiting can be prevented by providing such a mixed film in the patent document 1.
It is thought that the technique as disclosed in the patent document 1 is extremely effective to reduce short-circuiting caused between a pair of electrodes. However, with respect to absorption spectrum characteristics of the mixed film, in which divanadium pentoxide and α-NPD are mixed, there are large variations in absorption intensity being dependent on an absorption wavelength especially in a visible light region. Accordingly, the amount of light absorbed in the mixed film is varied depending on wavelengths of light emission, thereby causing; difference in light extraction efficiency for each wavelength of light emission.    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-123095